(It.: ‘single key’).
A phrase used by composers to instruct the keyboard player of a continuo part to play the bass note(s) alone, without chords above. The phrase seems to occur in music (e.g. Corelli op.5) before it is described in theory books (Heinichen, 1728, Pasquali, Albrechtsberger), where the player is directed to play only those notes, singly (Heinichen) or with their octave (Adlung) or (if long) restruck (C.P.E. Bach etc.). C.P.E. Bach noted that the Italians did not in practice ever play tasto solo. Many composers also gave figures for passages marked tasto solo and in this case the figures may merely indicate the harmony implied or stated above by other instruments; these are either for the continuo player to fill in if necessary or, as in the case of Bach’s cantata bass parts, for the sake of the copyist writing out a part from the full score. To distinguish single notes from those doubled at the octave above or below, C.P.E. Bach applied the phrases all’unisono and all’ottava, but only theorists and composers under his influence (e.g. G.S. Löhlein, 1791) made any use of them.
PETER WILLIAMS